The contest for control of Congress will come down to the outcomes in as many as 70 House and 11 Senate races spread across time zones from Maine to Alaska.

Polls in the first series of bellwether House districts begin closing at 6 p.m. Eastern time. Those will provide an initial glimpse into whether Democrats are building a "blue wave" that sweeps Republican out of power in Congress or GOP members are able to hang on to majorities in the House and Senate.

It's possible that control of Congress is settled before midnight, but the unusually large number of close contests, many in states known for slow ballot counting, means the first midterm of Donald Trump's presidency could go into overtime, perhaps for days after Nov. 6.

Here's a chronological guide to watching for the key races. All times are eastern.

6 p.m. – Indiana and Kentucky

Indiana and Kentucky are divided between the eastern and central time zones and there are key races in both where polls close at 6 p.m.

The first is Kentucky's 6th, a Republican-leaning area where Republican Representative Andy Barr and Democrat Amy McGrath, a former Marine fighter pilot, have raised at least $12.6 million between them — most of it by the challenger.

About 40 percent of the district vote comes of Fayette County in and around Lexington, which usually reports its votes early. That should be pro-McGrath along with Franklin County in and around Frankfort, the state capital. The district's more rural counties are strongly Republican.

A win by McGrath, in a district Trump won by 16 percentage points in 2016, would be an early sign of wider gains for Democrats, who need a net gain of 23 seats to overturn the Republican House majority.

In Indiana, Republican Representative Jackie Walorski is more politically secure in a district that Trump won by more than 20 percentage points in the 2016 election. An unexpectedly close race for Walorski could be an early warning sign for Republicans.

Indiana's Senate race is among the most competitive in the nation. Democratic Senator Joe Donnelly faces Republican Mike Braun, a wealthy businessman and former state legislator. A Donnelly loss probably would foreclose the Democrats' slender path to overturning the Republicans' Senate majority. Donnelly is one of five Democratic senators seeking re-election this year in a state Trump won by at least 18 percentage points.

7 p.m. – Virginia and Florida

Watch Virginia's 7th District, a Republican-leaning area near Richmond where Republican Representative Dave Brat is at risk of losing his seat to Democrat Abigail Spanberger, a former CIA officer.

The biggest source of votes in the district is suburban Chesterfield County, which tends to report its votes quickly. Spanberger may need about 54 percent of the vote in Chesterfield to offset Brat's expected advantages in more rural and Republican counties.

Vote-reporting is slower in northern Virginia, where Republican Representative Barbara Comstock is at risk of losing to Democratic state Senator Jennifer Wexton in the 10th District, a well-educated, high-income area that's trending Democratic.

It could be a terrible night for Republicans if they lose Virginia's 2nd District in and around Virginia Beach, or the open 5th District, which runs from exurbs of Washington south through Charlottesville all the way to the North Carolina border.

In Florida, districts worth watching include two Hispanic-majority areas with parts of populous Miami-Dade County. In the 26th District, look to see if Republican Representative Carlos Curbelo can again buck anti-Trump sentiment and survive in a Democratic upswing.

In the 27th District, former Health and Human Services Secretary Donna Shalala is favored to win the district of Representative Ileana Ros-Lehtinen, a popular moderate Republican who's retiring.

Florida also has a marquee Senate matchup between Democratic incumbent Bill Nelson and outgoing Republican Governor Rick Scott. Shortly after 7 p.m., look for Florida counties to report the results of their early-voting period, an increasingly popular method of casting ballots compared with voting on Election Day. In Florida's Republican-leaning Panhandle, polls close at 8 p.m. eastern.

There are crucial races in two other states in the 7 p.m. hour.

In South Carolina, the race to watch is in the 1st District, a Republican-leaning area in the Charleston area. Republican Katie Arrington, a pro-Trump state legislator who unseated Representative Mark Sanford in the primary, is up against Democrat Joe Cunningham, a lawyer and ocean engineer.

In Georgia, Republican Representatives Karen Handel and Rob Woodall are seeking new terms in suburban Atlanta districts that have a Republican history but were only mildly pro-Trump in 2016.

Handel narrowly won a special election last year and is in a close race against Democrat Lucy McBath, a gun-control activist. Woodall's 7th District is only 43 percent non-Hispanic white, and Democrat Carolyn Bourdeaux could benefit from a large turnout for Democratic gubernatorial nominee Stacey Abrams, who would be Georgia's first black governor and the first black woman to hold the post in any state.

7:30 p.m. – North Carolina, Ohio, West Virginia

Watch North Carolina's 9th District, which includes suburbs of Charlotte and leans Republican. Dan McCready, one of many Democratic veterans seeking House seats, faces Republican pastor Mark Harris after Harris unseated Republican Representative Robert Pittenger in the primary.

In West Virginia, Democratic Senator Joe Manchin is opposed by Republican state Attorney General Patrick Morrisey in a state that gave Trump his highest vote percentage in the nation — 69 percent. Manchin has held a steady lead in polls of the races, which Democrats are counting on as a buffer to possible losses elsewhere.

8 p.m. – Pennsylvania, New Jersey, Kansas

Voting ends in more than a dozen states including Pennsylvania, where Democrats could make big House gains under a congressional map imposed by the state Supreme Court to replace a Republican-drawn map it invalidated as an unlawful political gerrymander.

Watch the 1st District, dominated by suburban Bucks County near Philadelphia. Republican Representative Brian Fitzpatrick, who's opposed party leaders on environmental and labor policy, faces Democrat Scott Wallace, a wealthy philanthropist and grandson of former Vice President Henry Wallace.

Polls close in Missouri, New Jersey and Tennessee, and in parts of North Dakota and most of Texas. All five states have competitive Senate races. North Dakota Democrat Heidi Heitkamp may be the most vulnerable senator seeking re-election.

Democrats may win as many as four Republican-held districts in New Jersey. Democratic Senator Robert Menendez is laboring to keep his seat in the face of questions about his ethical conduct. Menendez's Republican opponent, former Celgene Corp executive Bob Hugin, spent at least $36 million of his money on the race. New Jersey last elected a Republican to the Senate in 1972.

Democrats are favored to win the southern 2nd District of retiring Republican Frank LoBiondo. They're also making strong takeover bids to unseat Republicans Tom MacArthur in the south-central 3rd District and Leonard Lance in the north-central 7th District and probably will win the northern 11th District of retiring Republican Rodney Frelinghuysen. The 7th and the 11th Districts take in parts of Morris County and are among the wealthiest and best-educated districts in the nation.

Democrats could pick up two seats in Republican-friendly Kansas.

9 p.m. – New York, Minnesota, Arizona

States to watch include New York, where several House Republicans are in close races, and Minnesota, where four of the eight districts are highly competitive.

In New York, Republican Representative John Faso faces Democrat Antonio Delgado in a mildly Republican-leaning district that includes part of the Hudson Valley and the Catskill region. Another first-term Republican, Claudia Tenney, is opposed by Democratic assemblyman Anthony Brindisi in the 22nd District, a pro-Trump area in 2016 that includes Utica and Binghamton.

Watch the Syracuse-based 24th District to see if Republican Representative John Katko survives the Democratic upswing. His district voted for Democrat Hillary Clinton over Trump, though Katko has bipartisan appeal.

Of the few opportunities nationwide for Republicans to win Democratic-held districts, two are in Minnesota. Republicans are targeting the southern 1st District of Tim Walz, who's running for governor, and the northeastern 8th District of Rick Nolan, who's not running again to represent the Iron Range.

Democrats may win from Republicans the suburban Twin Cities' districts of Representatives Jason Lewis and Erik Paulsen.

Arizona gives Democrats an opportunity to flip a Republican-held Senate seat. Democratic Representative Kyrsten Sinema and Republican Representative Martha McSally are vying to succeed Republican Jeff Flake.

10 p.m. – Iowa, Montana, Nevada, Utah

Watch Senate elections in Montana, another of the five states where a Democratic senator is seeking re-election in a strongly pro-Trump state, and Nevada, the only state where a Republican senator is seeking re-election in a state that voted Democratic for president.

Montana, where Democratic Senator Jon Tester is seeking a third term, also is hosting a competitive race for its statewide congressional district. Republican Representative Greg Gianforte, who won a special election last year after assaulting a reporter, faces Democratic state representative Kathleen Williams.

In Nevada, Republican Senator Dean Heller is trying to fend off first-term Democratic Representative Jacky Rosen. Democratic-leaning Clark County in and around Las Vegas provides most of the Nevada vote - 68 percent in 2012 and 2016, both good Democratic years, but just 62 percent in 2014, when Republicans dominated Nevada elections. Heller in 2012 was the only Republican Senate candidate elected in a state President Barack Obama carried.

Nevada's quintessential swing area is Washoe County in and around Reno; the Democratic-Republican percentages there usually come close to the statewide percentages.

In Utah, former Massachusetts Governor Mitt Romney is favored to win an open Senate seat. Romney, who won 72 percent of the vote in Utah when he ran for president in 2012, filmed a television commercial endorsing Republican Representative Mia Love, who's in a close race.

Iowa, which went from voting for Obama in 2012 to Trump in 2016 may be on the cusp of shifting again as three of four congressional districts are competitive. Democrats are seeking to unseat Republican Representatives Rod Blum in the 1st District, David Young in the 3rd District, and Steve King in the 4th District.

11 p.m. – California, Washington

Polls close in California, the nation's most populous state. Democrats are targeting all seven districts that voted Republican for the House and Democratic for president in 2016. Four of them take in parts of Orange County, an upper-income, well-educated and diversifying area that was once a Republican bastion.

Depending on how close the California contests are, it could be hours or even days before we know all of the winners. Many Californians now vote by mail, and those ballots may be postmarked as late as election day.

Washington state, which votes by mail, includes three House districts Democrats are seeking to wrest from Republican control.

12 a.m. – Alaska

Most polls close in Alaska, where Republican Representative Don Young has represented its single statewide district for more than 45 years. Young faces a serious challenger in Alyse Galvin, an education activist and political independent who won the Democratic primary. Alaska's vast geography -- it's more than twice as big as Texas -- doesn't lend itself to fast vote-counting, and it may take a while before we know the winner.